Proofed paper



April 24, 1928. 1 1,667,691.

J. REID PROOFED PAPER Filed Nov. 1926 INFUSED NON Hwy/5E0 LA YER LA ripsINVENTOR/ CHQJEI% MM.

ATTORNEYS Phtented Apr. 24, 1928.

UNITED STATES 1,661,691 PATENT m cs;

JAMES REID, OF MOUNT VERNON, NEW YORK, ASSIGNOR TO THE SCU'IAN COMPANY,A CORPORATION OF DELAWARE.

PROOFED PAPER.

Application filed November 28, 1926. Serial No. 150,868.

The resent invention relates to a proofed cellulosic product,particularly to a waterproof aper made from a paper having a base ofwood or cotton fibre. My inventlon is primarily directed to thetreatment of close grained materials such as paper as d1stinguished fromloose formed bodies suchas building felt. Accordingly, I broadly termthe basic material close grained cellulosie fibrous material. Y

My invention is based upon the d scovery that if proper precautions andconditions are had, it is possible to infuse the surface layers of asheet of close grained cellulo'sic fibrous material with a viscouscompound at a temperature which normally would substantially destroysuch material. By us ng such a'high temperature, a type of impregnationor infusion can be obtained which has never before been possible, withthe result that I can produce a product having markedly differentcharacteristics from those which have heretofore been made.

Ordinarily, if cellulosic fibrous material such as paper, the fibres ofwhich are unprotected, is exposed to a temperature substantially above250 F. it will be so carbonized that it will lose all its strength.According to my process such a material is plunged into a bath ofviscous proofing compound which has a temperature substantially above250 and preferably is above 400, under such conditions that the surfacelayers will be infused with the proofing agent, but the middle of thesheet will have lts fibres 'uncoated. In applying such a temperature tothe paper or similar material, great care must be taken to reduce theaccess of air. Also the time of treatment must be short 40 and after thetreatment, provisionmust be made for rapid cooling so that air does notcontact with uncoated fibres at carbonizing temperature. This can betaken care of by havlng a. web of paper or other fibrous ma- 1 terialwhich moves quite rapidly and plunges into a bath of molten but viscousproofing compound. The web should be submerged in the viscous compoundonly a short time and when it emerges the web should be stripped almostimmediately, so that the mass of viscous compound in the web is smalland the temperature may .drop promptly.

The proofing compound may be of various rubber or bituminous materialwhich I have used has a melting point above 250, for example, I may usea material having a melting point of from 290 to 310 F., ring and ballmethod. The scale wax, which is a paraflin product, has a melting pointof about 122. The Montan wax is a natural wax in'iported from Germany,and the type which I have used is a crude Wax, black 1n color, with amelting point of about 168. The mixed bath has a melting point of above250 F. and when cool has very little tackiness due to the presenceof-tfic waxes. I heat this bath to a temperature above 350 F.-say450---at which temperature it isliquid but still extremely viscous.

I believe that the phenomena which take place in my process are somewhatas follows, but I do not wish to limit myself to the theory herein setforth.

The web of fibrous material always contains a certain amount ofmoisture. As soon as the web enters the hot bath, -steam is evolved;The-steam escaping from the web forms a stiff but cellular coating overthe bath which I term a brat because of its resemblance-to the coatingwhich forms when cheese is made. In operation, the brat should beallowed to develop until it is several inches thick when the surfacewill be found to be quite cool. The brat serves to keep the heat in thebath and also serves as a protective coating through which the webpasses as it is being heated, so that the hot fibres are not exposed tothe air.

The team and entrained air will leave the web until the pressure in theweb equalizes the pressure in the bath which is a little aboveatmospheric, but a certain amount of air and superheated steam willremain in the web. The bath, although melted, is viscous and so the webwill absorb some of the'proofing agent but not as much as would be thecase ifa non-viscous liquid were being used. Apparently there is asubstantial infusion of the liquid between the fibres onthe surfaces ofthe web but only a negligible amount of permeation toward the center ofthickness.

- m In treating ordinary paper, I find that the.

web should be in the bath for only about five seconds where the bath isheated to a temperature of about 450 F. Under these conditions, infusiondoes not reach a maximum, with a rmult that in the finished prodnot thefibres of the center layers are substantially unaffected by the proofingmaterial. This gives to the finished product a high degree offlexibility, for the unproofed fibres of the center layers can moverelativelyto each other, permitting the surface layers to act more orless independently. For example, using kraft paper as a base, thefinished product can be creased and folded without cracking in the sameway as can be done with the unproofed paper. At the same time thebursting strength of the paper is somewhat increased. I

As the paper leaves the bath it is stripped of all surplus proofingmaterial. I prefer to do this stripping by the use of scrapers whichwill leave the paper at about its original thickness but the surfacewill be smoothed and polished and the thickness of the paper appears tobe more uniform. The relatively small amount of bituminous materialinfused through the surface portions will carry only a small amount ofheat and will permit the web to cool very rapidly. If a heavy paper isbeing treated, it may be advisable to cool the paper artificially as bypassing it over a chilled roll, for it must be remembered that themiddle fibres will be almost dry and are not individually protected bycoating material, so that they will filickly carbonize ifopportunity isiven. s cooling takes place, there must e a shrinkage in the gas contentat the center of thickness (which will be accentuated by condensation ofany residual moisture) will create a strong suction on the infusedsurfaces, drawing the proofing material closely around the fibres andprobably drawing a certain amount into the actual cells or tubes of thefibres. It is my belief that this suction action is strong enough tocause minute perforations to be formed in the surface, for when thecoated web is first formed and stripped, its strength will be markedlyless than will be the case after twenty-four hours when the web has hadan opportunity to reabsorb its normal complement of water. It may bethatas soon as the moisture content of the fibres reaches equilibrium, thecolloidal surface infusion will flow together closing the minute pores,for the final prodnot isfound to be extremely impervious to Water and tohave excellent dielectric quali ties.

In the accompanying drawing, I show a copy of a microphotograph of asection of kraft paper infused with bituminous mate-,

rial in accordance with the process that I of the web, This shrinkagehave described. This drawing emphasizes the manner in which the surfacefibres of the paper are thoroughly coated with the infused proofingagent, while the center is left substantially free.

The amount of proofing material that is infused into the surfaceportions of the paper may be varied with the temperature, time oftreatment. etc. but for general results I have found it .advisable toincorporate from 15% to 35% of proofing material (based on the weight ofthe finished prod net). This will give a product with about one-third toone-quarter of its thickness noninfused. The amount of infused materialmay be determined by treating the paper with appropriate solvents whichwill leave ing waterproof bags or containers or as a strongwaterproofwrapping where a fixed moisture content is to be maintained,or where dryness is essential as with explosives and some chemicals; ithas sufficient strength and a proper surface sov it can be embossed tomake a waterproof imitation leather, and its flexibility permits it tobe used for making cheap umbrellas. These examples are given only asillustrations of the many and widely varied uses to which the productmay be put.

Thus far I have described my product and process as one in which bothsurface layers of the paper are infused with the proofing agent. This isthe preferred embodiment of my invention, but in some instancesvaluableresults can be obtained if only one surface is proofed. This can be doneby passing the paper over a proofing roll a part of wvhich extends downinto a bath of the hot proofing agent. In this case no brat is formedbut burning .is prevented by reducing the time of application. A portionof the hot proofing agent will pass into the paper and volatilize themoisture from the fibres at the high temperature used. Infusion will besomewhat more rapid than wherethe paper is passed into a bath, as thesteam will not be entrapped. The surplus is stripped off and the paper,as before, allowed to cool quickly causing the proofing agent to bedrawn intothe pores of the fibres to replace the volatilized moisture.The amount of proofing agent used should be about the same as in theother case, from one-quarter to one-third of the paper being leftnon-infused.

1 What I claim is:

1. A process of proofing close-grained paper of substantial strength.and flexibility without destroying such flexibility and strength, whichcomprises" the steps of assing a sheet of such paper through a ath ofrelatively high melting point proofing material of a bituminous natureheated to a temperature substantially above 250 F., and until the bathis liquid but still viscous, and removing the sheet from ,the bathbeforeit is saturated with the proofing material. I

2. A process as defined in claim 1, in which the proofing materialcomprises a major proportion of bituminous. material having a meltingpoint above 290 F. and the bath is heated above 400 F.

3. A process as defined in claim 1, in which the bath comprise s'amixture of-bituminous material and wax.

4. The process of producing a proofed flexible sheet of papersubstantially unaffected by atmospheric temperatures which comprises thesteps ofpassing a substantially homogeneous flexible and relatively thinsheet of close-grained fibrous cellulosic material through a bath ofrelatively high melt; ing point proofing material of a bituminous natureheated to a temperature substantially above 250 F. and until the bath isliquid, removing the sheet from the bath before it is entirely saturatedwith the proofing material, stripping off surplus proofing material andcausing the sheet to cool rapidly whereby the cellulosic material isproofed and given a firm surface without having its strength orflexibility substantially injured.

5. A process of producing highly flexible proofed paper with a non-tackysurface which comprises the steps of infusing into the surface of asheet of close grained fibrous cellulosic material less than enoughrelatively high melting point bituminous proofing agent to permeate theentire thickness of the sheet by contacting the paper with the proofingagent in an extremely viscous statebut at a temperature substantiallyabove 250 F., withdrawing the paper from the mass of proofing agentbefore it is fully infused, stripping off surplus proofing material andcausing the sheet to cool rapidly.

6. A process of producin proofed paper which comprises the steps 0heat-ing a muture of bituminous material and wax to a.

temperature above 350 F., causing a rela-.

terial a surface layer of which is infusedwith a bituminous proofingmaterial which has a melting point above 250 F. and which has a layerwhich is non-infused, the infused layer being substantially non-tacky atatmospheric temperatures.

8. A product as defined in claim 7, in which'both surface layers areinfused and the center portion is non-infused.

9. A product as defined in claim 7 in which the fibrous cellulosicmaterial is paper and the proofing material comprises a major portion ofbituminous material having a melting point above 290 F.

10. A new product of considerable strength and with flexibilitycorresponding to t at of paper, comprising paper the surface layers ofwhich are infused with a bituminous proofing agent which issubstantially nontacky at atmospheric temperatures and comprises a majorportionof bituminous material having a melting point above 290'F., whilethe center layers are substantially non-infused.

11. A product as defined in claim 10, in which the paper containing theinfused proofing agent is substantially the same thickness as the paperwithout such agent.

'12. A product as defined ,in claim 10, in which from one-quarter toone-third of the paper is non-infused.

13. A product as defined in claim '10, in whichthe proofing agentconstitutes from 15 to 35% by weight of the product.

JAMES REID.

